1. Field of the Invention
The present invention relates to a semiconductor device, and more particularly, to an input circuit for a semiconductor device having a fuse for selective activation/deactivation of circuits, for example protective circuits, therein, and a semiconductor device incorporating such an input circuit.
2. Description of the Related Art
Throughout the evolution of semiconductor devices, the level of integration has steadily and dramatically increased to the point where presently, 64 Megabyte (Mb) Dynamic Random Access Memories (DRAMs) are routinely fabricated. In general, as integration increases, so too does device complexity, and therefore, despite advancements in integration, device size can increase. As a consequence, this demand for larger device sizes, coupled with the demand for heightened integration, is often accompanied by the need for development of new technology in related fields, such as photolithography, which carries with it high cost and reduced device yield.
To address this issue, "stack-type" packages have recently been proposed, suitable for improving the integration of a semiconductor device by more than two fold. Here, the stack-type package refers to both a chip-stack package in which at least two integrated circuit chips are stacked within a single package, and a package-stack package in which at least two packages, each having a chip incorporated therein, are stacked. In this manner, the effective device capability is doubled, while maintaining the same footprint.
For example, in a chip-stack package, two 128 Mb memory chips may be mounted within a single package to provide a 256 Mb memory chip. Alternatively, in a package-stack package, two individually-packaged 128 Mb chip packages may be stacked, thereby likewise providing a 256 Mb memory chip. In this manner, with either form of stack-type package, the integration level can be doubled using conventional processing technology, without the need for advancement of the technology.
As a result of the stack-type package configuration, each external package pin is shared by circuits residing on two separate memory chips. Consequently, the input capacitance value as seen by the external pin increases. In the case of two stacked packages, for example, corresponding external pins are electrically connected to each other so that the load applied to the input circuit connected to the respective external pins is double that of the single individual packages. This results in a reduction in transmission speed for signals traversing the external pin.